The majority of all centrifugal pumps have an inlet port in the center region of the spiral housing and an outlet port on its periphery so that the axes form a 90 degree angle. Pumps of this type are known as "centerline" pumps. It is desirable for many installations to have the inlet and outlet port on opposite sides. These types of pumps are known as "inline" pumps. If a centerline pump must be replaced, it can be done only with another centerline pump. On the other hand, more and more modern installations use inline pumps. Pump users which use both systems, such as most chemical plants, therefore must have replacement pumps of both types in stock. It is desirable to have one pump which can serve both purposes.